� In the Delta , the majority of irrigators are groundwater irrigators , where irrigation water recharges the aquifer and is subsequently reused to maintain soil moisture requirements .
� Delta growers apply more water per unit of area ( e . g . 20 + ML / ha ) than BRIA growers ( e . g . 10-12ML / ha ). Reasons include high soil permeability ( irrigation water leaches quickly ) in the Delta and most of the irrigation water is charged via area ($/ ha – not a volumetric charge ) in the Delta . These factors affect the relative economic benefit accrued from improvements in water application efficiency .
� There are 347 farms in the BRIA and 580 farms in the Delta ( see Table 3.1 ). The average farm size in the BRIA is 140ha ( with areas up to 3,500ha ) compared to 72ha in the Delta ( with areas up to 500ha ). Previous economic analysis conducted by Smith ( 2015 ) indicates that it is more cost effective to implement improved nutrient and irrigation management practices on the larger farms as fixed costs are spread across a larger production base .
Table 3.1 . Key characteristics of the BRIA and Delta sugarcane growing areas in the Lower Burdekin . Reproduced from Waterhouse et al . ( 2016 ) with inclusion of more recent updates .
Characteristic |
BRIA |
Delta |
Area |
49,222 ha |
41,262 ha |
Establishment |
Since 1980 ’ s |
Since 1880 ’ s |
Number of farms |
347 |
580 |
Approx Farm size 1
Dominant soils
Up to 3,500ha Median farm size : 94ha Average farm size : 140ha Sodic duplex / and light to medium and heavy clays ( high denitrification potential )
Up to 500ha Median farm size : 56ha Average farm size : 72ha Coarse sands , sandy loams and light to medium clays ( Low denitrification potential )
DIN loss pathway |
Large proportion in surface runoff |
Large proportion in drainage |
Modelled annual average DIN |
460t / yr |
586t / yr |
load 3
|
|
|
Average production 2
|
110 tonnes per ha |
120 tonnes per ha |
Fertiliser application rates 4
|
214 kgN / ha Plant |
193 kgN / ha Plant |
|
227 kgN / ha Ratoon |
216 kgN / ha Ratoon |
Water source and use |
Surface water and ground water in |
Ground water and surface water |
|
Northcote , Jardine and Selkirk areas |
from Water Board supply |
|
10-12 ML / ha |
20 + ML / ha |
|
Volumetric charge for water |
Largely area based charges for water |
|
Gravity fed systems leading to lower |
Pumping leads to higher electricity |
|
electricity costs |
costs |
Irrigation systems |
Predominantly furrow irrigation |
Predominantly furrow irrigation |
Data sources : |
|
|
|
1
Wilmar ( P . Larsen , pers . comm .), September , 2018 . Data extracted from end of 2017 harvest season .
|
|
2
Wilmar ( P . Larsen , pers . comm .), March 2016 .
|
|
3
Based on modelled estimates of DIN loads from sugarcane areas using the Paddock to Reef Source Catchments model ,
|
DNRM ( 2015 ). |
|
4
Paddock to Reef program Survey data , NQ Dry Tropics ( 2016 ).
|
3.2 Priority pollutants
The dominant water quality issues from sugarcane areas are DIN and pesticides , particularly PSII herbicides ( NQ Dry Tropics , 2016 ; Waterhouse et al ., 2016 , 2017a , b ).
Note that DNRME are currently updating the pollutant load estimates based on the latest Paddock to Reef program data update , and this will be provided when available ( likely to be late 2018 / early 2019 ). The data presented is from the Burdekin WQIP 2016 ( Source Catchments 2015 model run ). Since this time , Fraser et al . ( 2017 ) have developed a daily empirical runoff DIN concentrations model with updated inputs from local experimental data , which will be incorporated into the basic cropping system model ( APSIM ), leading to further improvements in the pollutant load estimates .
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